1. Field of the Invention
The present invention relates to a tandem pump having a pair of pump rotors in a hollow chamber of a pump housing.
2. Description of the Prior Art
A conventional tandem pump of this type, as illustrated in FIG. 5, is provided with a first cam ring 3, an intermediate side plate 4, a second cam ring 5, and a rear side plate 6 which are disposed side by side in order, and inserted in a hollow chamber 2 of a pump housing 1. Within the first cam ring 3 is rotatably disposed a first rotor 7 and within the second cam ring 5 is rotatably disposed a second rotor 8.
Between the rear side plate 6 and the end wall of the pump housing 1 are formed first and second fluid chambers 9a and 9b. The rear side plate 6 is pressed toward the second cam ring 5 and the second rotor 8 by means of a fluid presure of a fluid led into the first and second fluid chambers 9a and 9b. Furthermore, the intermediate side plate 4 is pressed toward the first cam ring 3 and the first rotor 7 and, at the same time, the rear side plate 6 is elastically deflected at the central part toward the second rotor side in order to reduce a gap, thereby preventing oil leaks from the sliding contact part.
In a conventional tandem pump of such a constitution, however, the inner peripheral part of the intermediate side plate 4 can not be elastically deflected, depending upon the fluid pressure of the discharge fluid led into the first and second fluid chambers 9a and 9b. Accordingly, oil leaks through a gap between this intermediate side plate 4 and the first and second rotors 7 and 8 can not reliably be prevented, resulting in such a problem as poor volumetric efficiency.
An accessory drive mechanism having a separator plate in contact with a pump rotor and a motor rotor has been disclosed in U.S. Pat. No. 3,104,530, and a hydraulic pump having a pressure plate in contact with a pump rotor has been disclosed in U.S. Pat. No. 4,347,047.